Compression molding is a method of molding in which the molding material, generally preheated, is first placed in an open, heated mold cavity. The mold is closed with a top force or plug member, pressure is applied to force the material into contact with all mold areas, while heat and pressure are maintained until the molding material has cured. The process employs thermosetting resins in a partially cured stage, either in the form of granules, putty-like masses, or preforms.
Compression molding is a high-volume, high-pressure method suitable for molding complex, high-strength fiberglass reinforcements. Advanced composite thermoplastics can also be compression molded with unidirectional tapes, woven fabrics, randomly orientated fiber mat or chopped strand. The advantage of compression molding is its ability to mold large, fairly intricate parts.
Also, it is one of the lowest cost molding methods compared with other methods such as transfer molding and injection molding; moreover it wastes relatively little material, giving it an advantage when working with expensive compounds. However, compression molding often provides poor product consistency and difficulty in controlling flashing, and it is not suitable for some types of parts.
Compression molding produces fewer knit lines and less fiber-length degradation than injection molding. Compression-molding is also suitable for ultra-large basic shape production in sizes beyond the capacity of extrusion techniques. Materials that are typically manufactured through compression molding include: Polyester fiberglass resin systems (SMC/BMC), Torlon PAI, Vespel PI, Meldin PI, Ryton PPS, and many grades of PEEK.
Compression molding was first developed to manufacture composite parts for metal replacement applications, compression molding is typically used to make larger flat or moderately curved parts. This method of molding is greatly used in manufacturing automotive parts such as hoods, fenders, scoops, spoilers, as well as smaller more intricate parts. The material to be molded is positioned in the mold cavity and the heated platens are closed by a hydraulic ram.
Bulk molding compound (BMC) or sheet molding compound (SMC), are conformed to the mold form by the applied pressure and heated until the curing reaction occurs. SMC feed material usually is cut to conform to the surface area of the mold. The mold is then cooled and the part removed.
Materials may be loaded into the mold either in the form of pellets or sheet, or the mold may be loaded from a plasticating extruder. Materials are heated above their melting points, formed and cooled. The more evenly the feed material is distributed over the mold surface, the less flow orientation occurs during the compression stage.
Thermoplastic matrices are commonplace in mass production industries eg. automotive applications where the leading technologies are Long Fibre reinforced Thermoplastics (LFT) and Glass fiber Mat reinforced Thermoplastics (GMT).
In compression molding there are six important considerations that an engineer should bear in mind:
Determining the proper amount of material.
Determining the minimum amount of energy required to heat the material.
Determining the minimum time required to heat the material.
Determining the appropriate heating technique.
Predicting the required force, to ensure that shot attains the proper shape.
Designing the mold for rapid cooling after the material has been compressed into the mold.
Compression molding is one of the original processing methods for manufacturing plastic parts developed at the very beginning of the plastics industry. In fact, it was widely used in the bakery industry for cookie or cake molding before plastic materials existe
There are four main steps to the thermoset composite compression molding process:
1) A high strength, two part metallic tool is created that exactly matches the dimensions required to produce the desired part. The tool is then installed in a press and heated.
2) The desired composite is pre-formed into the shape of the tool. Pre-forming is a crucial step that helps to improve the performance of the finished part.
3) The pre-formed part is inserted into the heated mold. The tool is then compressed under very high pressure, usually ranging from 800psi to 2000psi (depending on the thickness of the part and the type of material used).
4) The part is removed from the tool after the pressure is released. Any resin flash around the edges is also removed at this time.
Compression molding is a popular technique for a number of reasons. Part of its popularity stems from its use of advanced composites. These materials tend to be stronger, stiffer, lighter, and more resistant to corrosion than metal parts, resulting in superior objects. Manufacturers accustomed to working with metal parts find that it is very simple to convert an object designed for metal into a compression molding part. Because it is possible to match metal part geometry with this technique, in many circumstances one can simply drop-in and replace the metal part altogether.
Another advantage of compression molding is its ability to create very complex parts. While this technique can not quite reach the production speed of plastic injection molding, it does offer more intricacies in geometry than typical laminated composites. It also allows for longer fibers than plastic injection molding, resulting in stronger and stiffer materials. Therefore, compression molding can be seen as a middle ground between plastic injection molding and laminated compound fabrication.
With its ability to create complex parts with a huge variety of applications while keeping part cost and turnaround time a priority, compression molding is an advantageous process for manufacturers in a wide range of industries.
compression molding is one of molding method, your introduction is very good
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compression molding is not the mainstream of the molding industry
compression molding is one of molding method，Compared with injection molding, it is not very popular
this kind of molding method is often used in our company
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thank you for your introduction, compression molding is often used in our company
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